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- PublicationOpen AccessObserved shift towards earlier spring discharge in the main Alpine rivers(2015)
; ; ; ; ;Zampieri, M.; CMCC ;Scoccimarro, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Gualdi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Navarra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; ; ; In this study, we analyse the observed long-term discharge time-series of the Rhine, the Danube, the Rhone and the Po rivers. These rivers are characterised by different seasonal cycles reflecting the diverse climates and morphologies of the Alpine basins. However, despite the intensive and varied water management adopted in the four basins, we found common features in the trend and low-frequency variability of the spring discharge timings. All the discharge time-series display a tendency towards earlier spring peaks of more than two weeks per century. These results can be explained in terms of snowmelt, total precipitation (i.e. the sum of snowfall and rainfall) and rainfall variability. The relative importance of these factors might be different in each basin. However, we show that the change of seasonality of total precipitation plays a major role in the earlier spring runoff over most of the Alps.567 368 - PublicationOpen AccessThe Role of Forcings in the Twentieth-Century North Atlantic Multidecadal Variability: The 1940–75 North Atlantic Cooling Case StudyResults from a study inspecting the origins of multidecadal variability in the North Atlantic sea surface temperature (NASST) are presented. The authors target in particular the 1940–75 “warm-to-cold” transition, an event that is generally framed in the context of the longer-term Atlantic multidecadal variability (AMV) cycle, in turn associated with the Atlantic meridional overturning circulation (AMOC) internal variability. Here the authors examine the ability of uninitialized, historical integrations from the phase 5 of the Coupled Model Intercomparison Project (CMIP5) archive to retrospectively reproduce this specific episode of twentieth-century climatic history, under a hierarchy of forcing conditions. For this purpose, both standard and so-called historical Misc CMIP5 simulations of the historical climate (combining selected natural and anthropogenic forcings) are exploited. Based on this multimodel analysis, evidence is found for a significant influence of anthropogenic agents on multidecadal sea surface temperature (SST) fluctuations across the Atlantic sector, suggesting that anthropogenic aerosols and greenhouse gases might have played a key role in the 1940–75 North Atlantic cooling. However, the diagnosed forced response in CMIP5 models appears to be affected by a large uncertainty, with only a limited subset of models displaying significant skill in reproducing the mid-twentieth-century NASST cooling. Such uncertainty originates from the existence of well-defined behavioral clusters within the analyzed CMIP5 ensembles, with the bulk of the models splitting into two main clusters. Such a strong polarization calls for some caution when using a multimodel ensemble mean in climate model analyses, as averaging across fairly distinct model populations may result, through mutual cancellation, in a rather artificial description of the actual multimodel ensemble behavior. A potentially important role for both anthropogenic aerosols and greenhouse gases with regard to the observed North Atlantic multidecadal variability has clear implications for decadal predictability and predictions. The uncertainty associated with alternative aerosol and greenhouse gas emission scenarios should be duly accounted for in designing a common protocol for coordinated decadal forecast experiments.
68 118 - PublicationOpen AccessDecadal climate predictions with a coupled OAGCM initialized with oceanic reanalyses(2013-03)
; ; ; ; ; ; ; ; ; ;Bellucci, A.; Ctr Euromediterraneo Cambiamenti Climat, I-40127 Bologna, Italy ;Gualdi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Masina, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Storto, A.; Ctr Euromediterraneo Cambiamenti Climat, Bologna, Italy ;Scoccimarro, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Cagnazzo, C.; CNR, Rome, Italy ;Fogli, P.G.; Ctr Euromediterraneo Cambiamenti Climat, I-40127 Bologna, Italy ;Manzini, E.; Max Planck Inst Meteorol, D-20146 Hamburg, Germany ;Navarra, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; ; ; ; ; ; ; ; We investigate the effects of realistic oceanic initial conditions on a set of decadal climate predictions performed with a state-of-the-art coupled ocean-atmosphere general circulation model. The decadal predictions are performed in both retrospective (hindcast) and forecast modes. Specifically, the full set of prediction experiments consists of 3-member ensembles of 30-year simulations, starting at 5-year intervals from 1960 to 2005, using historical radiative forcing conditions for the 1960-2005 period, followed by RCP4.5 scenario settings for the 2006-2035 period. The ocean initial states are provided by ocean reanalyses differing by assimilation methods and assimilated data, but obtained with the same ocean model. The use of alternative ocean reanalyses yields the required perturbation of the full three-dimensional ocean state aimed at generating the ensemble members spread. A full-value initialization technique is adopted. The predictive skill of the system appears to be driven to large extent by trends in the radiative forcing. However, after detrending, a residual skill over specific regions of the ocean emerges in the near-term. Specifically, natural fluctuations in the North Atlantic sea-surface temperature (SST) associated with large-scale multi-decadal variability modes are predictable in the 2-5 year range. This is consistent with significant predictive skill found in the Atlantic meridional overturning circulation over a similar timescale. The dependency of forecast skill on ocean initialization is analysed, revealing a strong impact of details of ocean data assimilation products on the system predictive skill. This points to the need of reducing the large uncertainties that currently affect global ocean reanalyses, in the perspective of providing reliable near-term climate predictions.340 189 - PublicationOpen AccessThe role of Mediterranean mesoscale eddies on the climate of the Euro-Mediterranean region(2011-04)
; ; ; ; ; ; ;Bellucci, Alessio; CMCC ;Gualdi, Silvio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Scoccimarro, Enrico; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Sanna, Antonella; CMCC ;Oddo, Paolo; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Navarra, Antonio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; ; ; ; ; Within the CIRCE (Climate Change and Impact Research: The Mediterranean Environment) EU Project, substantial efforts were devoted to enhance the representation of the oceanic system in the Mediterranean region. This was achieved by developing coupled general circulation models with ocean components which either explicitly resolve, or simply permit, mesoscale circulation features. The inclusion of the eddy variability tail in the spectrum of the processes resolved by the modelled system represents a particularly relevant step forward with respect to the previous CMIP3 generation of climate models , as these were systematically based on coarse resolution ocean components, leading in turn to an extremely rough representation of the Mediterranean Sea sub-system. In this study the role of mesoscale oceanic features on the air-sea interactions over the Mediterranean region was analysed, in the context of one of the CIRCE ensemble of climate models. To this aim, two different simulations of the 20th Century climate, performed with two distinct configurations of the CMCC coupled general circulation model featuring radically different horizontal resolutions in the Mediterranean Sea domain, were compared. This comparison highlights the implications deriving from the inclusion of energetic ocean mesoscale structures in the variability spectrum of the coupled ocean-atmosphere system and points to the need for high-resolution ocean components in the development of next generation climate model.270 121 - PublicationOpen AccessMulti-model assessment of the late-winter extra-tropical response to El Niño and La Niña(2022)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; El Niño-Southern Oscillation (ENSO) is known to affect the Northern Hemisphere tropospheric circulation in late-winter (January–March), but whether El Niño and La Niña lead to symmetric impacts and with the same underlying dynamics remains unclear, particularly in the North Atlantic. Three state-of-the-art atmospheric models forced by symmetric anomalous sea surface temperature (SST) patterns, mimicking strong ENSO events, are used to robustly diagnose symmetries and asymmetries in the extra-tropical ENSO response. Asymmetries arise in the sea-level pressure (SLP) response over the North Pacific and North Atlantic, as the response to La Niña tends to be weaker and shifted westward with respect to that of El Niño. The difference in amplitude can be traced back to the distinct energy available for the two ENSO phases associated with the non-linear diabatic heating response to the total SST field. The longitudinal shift is embedded into the large-scale Rossby wave train triggered from the tropical Pacific, as its anomalies in the upper troposphere show a similar westward displacement in La Niña compared to El Niño. To fully explain this shift, the response in tropical convection and the related anomalous upper-level divergence have to be considered together with the climatological vorticity gradient of the subtropical jet, i.e. diagnosing the tropical Rossby wave source. In the North Atlantic, the ENSO-forced SLP signal is a well-known dipole between middle and high latitudes, different from the North Atlantic Oscillation, whose asymmetry is not indicative of distinct mechanisms driving the teleconnection for El Niño and La Niña.66 33 - PublicationRestrictedThe influence of the Indian Ocean on the Eastern Mediterranean interannual variability, as simulated by a coupled general circulation model(2010-09)
; ; ; ;Roxy, Mattew; CMCC ;Gualdi, Silvio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Scoccimarro, Enrico; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; ; The interannual variability of the teleconnection between the Eastern Mediterranean (EM) and the Indian Ocean is investigated using 20th century simulations conducted with a fully coupled high-resolution global general circu- lation model, and the European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40). Comparison with observations, reanalysis, and model simulations shows that, though the model results slightly underestimate the magnitude of the anomalies, they provide a reliable representation of its real space and time va-riability. The model appears to be able to reproduce the observed Eastern Mediterranean climate variability and the associated variability over the Indian Ocean and the Indian subcontinent. Composite analysis of the vertical ve- locity anomalies over the Eastern Mediterranean shows that the subsidence over these regions is increased with the occurrence of positive Indian Ocean Di-pole (IOD) events. It is found that, both in the model and the reanalysis, a positive IOD results in an anomalous meridional overturning circulation between the tropical eastern Indian Ocean and the Indian Subcontinent. This meridional circulation connects an anomalous descent (ascent) branch over the Indian Ocean (Indian subcontinent). The anomalous meridional circulation in turn triggers a rossby wave response to the west of the ascending branch at about 200 hPa, inten-sifying the subsidence over the EM95 23 - PublicationOpen AccessDevelopment of a numerical model of sea ice for biogeochemical studies. Part 1: Sea-ice thermodynamics(2007)
; ; ; ; ;Tedesco, L.; CMCC ;Vichi, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Haapala, J.; Finnish Institute of Marine Research, Helsinki, Finland ;Stipa, T.; Finnish Institute of Marine Research, Helsinki, Finland; ; ; A fully prognostic 1-D thermodynamic model, functional for studies of sea-ice biogeochemistry is developed to better understand the physical processes and the interactions between the environment and the sea-ice ecosystem. The physical model is capable of simulating seasonal changes of snow and ice thickness. Particular attention is paid to reproduce the snow-ice and the superimposed ice formation which play important roles in the dynamics of sea ice algae. The assessment of the model capabilities is done in 1979--1993 at four different stations in the Baltic Sea. A sensitivity analysis stresses the importance of adequate surface forcing functions to properly simulate the onset of sea ice. Our results show that thickness of the ice layers and timing of the melting are in good agreement with the observed data and confirm that one of the key variables in modelling sea-ice thermodynamics is the snow layer and its metamorphism.228 222 - PublicationRestrictedA Multisystem View of Wintertime NAO Seasonal PredictionsSignificant predictive skill for the mean winter North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) has been recently reported for a number of different seasonal forecasting systems. These findings are important in exploring the predictability of the natural system, but they are also important from a socioeconomic point of view, since the ability to predict the wintertime atmospheric circulation anomalies over the North Atlantic well ahead in time will have significant benefits for North American and European countries. In contrast to the tropics, for the mid latitudes the predictive skill of many forecasting systems at the seasonal time scale has been shown to be low to moderate. The recent findings are promising in this regard, suggesting that better forecasts are possible, provided that key components of the climate system are initialized realistically and the coupled models are able to simulate adequately the dominant processes and teleconnections associated with low-frequency variability. It is shown that a multisystem approach has unprecedented high predictive skill for the NAO and AO, probably largely due to increasing the ensemble size and partly due to increasing model diversity. Predicting successfully the winter mean NAO does not ensure that the respective climate anomalies are also well predicted. The NAO has a strong impact on Europe and North America, yet it only explains part of the interannual and low-frequency variability over these areas. Here it is shown with a number of different diagnostics that the high predictive skill for the NAO/AO indeed translates to more accurate predictions of temperature, surface pressure, and precipitation in the areas of influence of this teleconnection.
68 4 - PublicationOpen AccessEffect of Tropical Cyclones on Ocean Heat Transport as simulated by a High Resolution Coupled GCM(2010-05)
; ; ; ; ; ; ;Scoccimarro, Enrico; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Gualdi, Silvio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Bellucci, Alessio; CMCC ;Sanna, Antonella; CMCC ;Oddo, Paolo; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Navarra, Antonio; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; ; ; ; ; This study investigates the Tropical Cyclone (TC) effect on the northern hemisphere Ocean Heat Transport (OHT) and the possible changes that greenhouse induced global warming might generate in the characteristics of the TC-induced OHT (TCiOHT). The analysis has been performed using 20C3M (20th Century) and A1B (21st Century) IPCC scenario climate simulations obtained running a fully coupled high-resolution global general circulation model named CMCC_MED. The Atmospheric model component has a T159 horizontal resolution and 31 vertical levels. The Ocean model component has a horizontal resolution ranging from 2 degrees to 0.5 degrees near the equator and 31 vertical levels. The capability of the model to reproduce a reasonably realistic TC climatology has been assessed by comparing the model results from the simulation of the 20th Century with observations. TC detection method has been implemented thanks to the TC-MIP project. The model appears to be able to simulate tropical cyclone-like vortices with many features similar to the observed TCs. The simulated TC activity exhibits realistic structure, geographical distribution and interannual variability, suggesting that the model is able to reproduce the major basic mechanisms that link the TC activity with the large scale circulation. The TC-induced ocean cooling is well represented and the resulting column-integrated ocean heating makes the poleward OHT larger in the subtropics and decreases the poleward heat transport out of the deep tropics. This effect, investigated looking at the 100 most intense Northern Hemisphere TCs, is strongly correlated to the TC-induced momentum flux at the surface of the ocean: the winds associated to the TCs significantly weaken the trade winds in the 5-18N latitude belt and reinforce them in the 18-30N band. TCs frequency and intensity appear to be substantially stationary through the whole 1950-2069 period. The effect of the TCs on the OHT is overall less pronounced in the 21st century when compared to the 20th century.175 260 - PublicationOpen AccessThe impact of the AMV on Eurasian summer hydrological cycle(2020)
; ; ; ; ; ; ; ; ; Impact studies of the Atlantic Multidecadal Variability (AMV) on the climate system are severely limited by the lack of sufficiently long observational records. Relying on a model-based approach is therefore mandatory to overcome this limitation. Here, a novel experimental setup, designed in the framework of the CMIP6-endorsed Decadal Climate Prediction Project, is applied to the CMCC climate model to analyse the remote climate impact of the AMV on the Northern Eurasian continent. Model results show that, during Boreal summer, an enhanced warming associated to a positive phase of the AMV, induces a hemispheric-scale wave-train response in the atmospheric circulation, affecting vast portions of Northern Eurasia. The overall AMV-induced response consists in an upper-tropospheric anomalous flows leading to a rainfall increase over Scandinavia and Siberia and to an intensified river runoff by the major Siberian rivers. A strengthening of Eurasian shelves' stratification, broadly consistent with the anomalous river discharge, is found in the proximity of the river mouths during positive-AMV years. Considering that Siberian rivers (Ob', Yenisei and Lena) account for almost half of the Arctic freshwater input provided by terrestrial sources, the implications of these findings for decadal variability and predictability of the Arctic environment are also discussed.47 10